Ion implantation systems are the mechanisms utilized to dope semiconductor substrates with dopants or impurities in integrated circuit manufacturing. In such systems, a dopant material is ionized and an ion beam is generated there-from. The beam is directed at the surface of a semiconductor wafer or workpiece in order to implant the wafer with one or more dopant elements. The ions of the beam penetrate the surface of the wafer to form a region of desired conductivity, such as in the fabrication of transistor devices in the wafer. A typical ion implanter includes an ion source for generating the ion beam, a beamline assembly including a mass analysis apparatus for directing and/or filtering (e.g., mass resolving) the ions within the beam using magnetic fields, and a target chamber containing one or more semiconductor wafers or workpieces to be implanted by the ion beam.
Ion implanters are advantageous because they allow for precision with regard to both quantity and placement of dopants within the silicon. In order to achieve a desired implantation for a given application, the dosage and energy of the implanted ions may be varied. The ion dosage controls the concentration of implanted ions for a given semiconductor material. Typically, high current implanters are used for high dose implants, while medium current implanters are used for lower dosage applications. Ion energy, on the other hand, is used to control the degree or depth to which ions are implanted into the workpiece, which can be useful in establishing different junction depths in semiconductor devices, for example.
One commercially available ion implantation system uses an ion source that includes a source chamber spaced from an implantation chamber where one or more workpieces are treated by ions from the source. An exit opening in the source chamber allows ions to exit the source so they can be shaped, analyzed, and accelerated to form an ion beam. The ion beam is directed along an evacuated beam path to the ion implantation chamber where the ion beam strikes one or more workpieces, typically generally circular wafers. The energy of the ion beam is sufficient to cause ions that strike the wafers to penetrate those wafers in the implantation chamber. Such selective implantation thus allows an integrated circuit to be fabricated.
It can be appreciated that the density of the ion beam or the number of ion per unit area in the beam is important to control. For example, it may be desirable to uniformly implant a workpiece with ions so that multiple devices formed upon/out of the workpiece operate in a consistent and predictable manner. In other instances it may be desirable to implant more dopant ions within some workpieces or areas of workpieces than others. In any event, it can also be appreciated that it is generally desirable to expedite fabrication processes to reduce costs, conserve resources and increase throughput and/or yield.